FIGS. 4 and 5 show a sealing structure of a casing of a conventional scroll fluid machine. FIG. 4 shows a scroll fluid machine disclosed in Japanese Patent Publication No. 6-65880 (Japanese Patent Laying-Open No. 60-190690), and FIG. 5 shows a scroll fluid machine disclosed in Japanese Patent Laying-Open No. 7-310677. For the purposes of convenience, components in FIGS. 4 and 5 related to those of the invention of the present application have reference characters allotted, and the labels thereof will be appropriately altered corresponding to the components of the invention of the present application.
Referring to FIG. 4, the casing of the scroll fluid machine is constituted by an upper casing 2a and a lower casing 2b. A fixed scroll 3, a movable scroll 4, a housing 5, a crank shaft 6, and a motor 22 are incorporated within the casing.
A compression chamber 15 for compressing gas refrigerant is formed of fixed scroll 3 and movable scroll 4. Movable scroll 4 includes a boss unit 4a and an outlet 4b for discharging compressed gas refrigerant. Crank shaft 6 includes an eccentric unit 6a into which boss unit 4a is inserted. A bearing metal 7a is provided between boss unit 4a and eccentric unit 6a.
Motor 22 includes a rotor 21 and a stator 20. Crank shaft 6 is inserted inside rotor 21. The peripheral portion of housing 5 is sandwiched between upper housing 2a and lower housing 2b. An O-ring 24 for sealing is attached at the boundary between housing 5 and upper casing 2a. A suction pipe 10 and a discharge pipe 23 are attached to the casing. The compressed gas refrigerant is discharged outside according to the open arrow in FIG. 4.
Referring to the conventional art of FIG. 5, a notch stepped portion 25 is provided in upper casing 2a to receive a peripheral portion 5a of housing 5. The lower end of upper casing 2a is fixed to the outer circumferential face of lower casing 2b by a welding portion 13. Housing 5 is secured by a spot welding portion 13a.
In the conventional art of FIG. 4, an O-ring 24 is provided between housing 5 and upper casing 2a. The usage of O-ring 24 induces the problem of increase in cost. In the case of FIG. 4, reduction in the spacing in the casing is a matter of concern since the open end of upper casing 2a is fitted into the inner side of the opening end of lower casing 2b.
In contrast, the problem of increase in cost due to usage of an O-ring is not encountered in the conventional case of FIG. 5 since no O-ring is used. Furthermore, the problem of reduction in the spacing in the casing is eliminated since upper casing 2a is outer-fitted to lower casing 2b. However, a welding process is carried out with respect to upper casing 2a and lower casing 2b. There is a possibility that housing 5 is deformed caused by deformation of upper and lower casings 2a and 2b by the welding process.